Aside from the tiny difference in length (muh room clearing) there are also people who live in states where all muzzle devices have to be pinned/welded anyway - therefore why not minimize barrel length in the process?

Muzzle devices don't make a great deal of difference anyway in 5.56, so the only downsides of not being able to swap them include suppressor attachments (though some QD attach directly to muzzle devices like Surefire's), and being able to remove gas block/gas tube (for swapping them out or changing handguard or barrel), for which there are things like the Faxon 14.5" with pinned slim muzzle devices that are same thickness as the barrel so you don't have to worry about the gas block removal question.

Pretty much - if you have your parts chosen and finalized, the only reason you'd need to be able to strip everything apart, which would be the issue if you have a pinned muzzle device, would be if you shot your barrel out. That is tens of thousands of rounds, or aka 'a lot more than most people will shoot in a lifetime'.